40x8 LCD display, one of the best keyboards ever made.
I see the custom keyboard community seem to be able to make any keyboard they like.
The keyboard on the Model 100 consumed the majority of its space, but at the same time, it was usable. I don't know what a reasonable display would be. The notable thing about the 40x8 is that it was big enough to be usable, and it was readable. I've seen some decks with tiny 640x480 displays, and they're not readable, particularly to my aging eyes.
The Psion 5 had a very usable keyboard, and better display than the M100. I don't know if that kind of keyboard can be made by a hobbyist like the other ones can. I don't know enough about keyboards. I don't know if one of those could be gutted and repurposed. (No doubt considered sacrilege to some.)
We see these "decks" with these matrices of buttons, but I'd dare say they're not really keyboards. The PET 2001 kind of proved that (and I did a lot of coding on a PET back in the day).
So, just curious what's stopping "real" ones, "nice" ones from showing up. I'd dare say money, but I see what folks spend money on for their hobbies, so it can't be that alone. Doesn't have to be a viable product for market.